Originally Posted by Frkl

I Second the gearing point. This could be mechanically compensated (new cassette and chainrings) or through unconsciously hanging out in different grars more. Also, slightly changing riding position can have a significant impact.

Crank length is but one lever in a system with lots of variable levers. It would be a lot easier to make generalization if we were riding penny farthings with the cranks directly attached to the wheel, and no real flexibility in riding position. Then, I could understand heated debates about categorical statements of the performance impact of going from 175 to 165 or even 150.

I think we are used to everything on a bike being adjustable--stem length and angle, saddle height, etc etc--except crank lengths. Changing crank length seems like a huge deal because we are used to thinking it's a given and a constant. But 175 is just as arbitrary as any other length i think. I mean, i would seriously doubt if all the component makers independently settled on 175 after having done exhaustive independent research which showed conclusively how much better it was than 176 or 174. More plausibly, someone at Shimano just chose it, corporate decided it made fiscal sense to phase out tooling for other lengths, and then other companies followed them like sheep. Consumers bought what was sold.

But imaging Shimano had settled on 156 for whatever reason. Then bikes, including gearing and angle and bb drop would be designed around that number (don't estimate how much the CPSC hates pedal strike!). And then 156 would start to seem really obvious and meaningful.